We report spherical neutron polarimetry (SNP) and discuss the spin-flip scattering cross sections as well as the chiral fraction η close to the helimagnetic transition in MnSi. For our study, we have developed a miniaturised SNP device that allows fast data collection when used in small angle scattering geometry with an area detector. Critical spin-flip scattering is found to be governed by chiral paramagnons that soften on a sphere in momentum space. Carefully accounting for the incoherent spin-flip background, we find that the resulting chiral fraction η decreases gradually above the helimagnetic transition reflecting a strongly renormalised chiral correlation length with a temperature dependence in excellent quantitative agreement with the Brazovskii theory for a fluctuation-induced first order transition.
@article{arxiv.1403.0551,
title = {Critical spin-flip scattering at the helimagnetic transition of MnSi},
author = {J. Kindervater and W. Häußler and M. Janoschek and C. Pfleiderer and P. Böni and M. Garst},
journal= {arXiv preprint arXiv:1403.0551},
year = {2014}
}